EP1245204B1 - Knee prosthesis - Google Patents

Abstract

A femur portion has center guide surfaces (20) for patella and a condyle (3) that can be pushed on separately. The femur portion has contact surface (6a) at an acute angle beta ( beta ) that can be pushed onto the resection area (7) at the stump of femur bone in the pivot range of the angle beta. The condyle center line is pivoted through angle about 15-60 degrees to allow greater flexion.

Description

The invention relates to a knee prosthesis with a femoral component, which has guide surfaces for a patella and at least one condyle, which outer contact surfaces at an acute angle α ≤ 90 ° and which along a straight line in the pivoting range of the angle α with contact surfaces on resection surfaces on the stump Femurbochens is pushed on. Document FR-A-2768329 discloses the features of the preamble of claim 1.

So far, it is customary in a knee prosthesis delay the condyles in the form of an upwardly open "U" on a pre-machined femur bone and secure. For this purpose, the femoral stump in the area of the natural condyles is brought to the shape of the contact surfaces of the artificial condylar parts, in order subsequently to fix them. The attachment itself can be made by projecting pins on the contact surfaces, by wedging the outer, opposing contact surfaces and / or by fixing the contact surfaces with bone cement. The condyles rest on a meniscal component or on a platform and can be pivoted on their running surfaces by a flexion angle δ during the articulation of the knee joint relative to the platform or to the tibia.

In EP-A-0 519 873 artificial knee joints are shown in which, depending on the condition of the ligaments, more or less effective lateral guidance of the condyles during articulation is possible.

The upper half of the prosthesis has guide surfaces for an anterior patella, and during flexion, the patella, which is offset by about 90 ° from the platform, slides on its own guide surfaces on the upper half of the prosthesis. The support surfaces of the upper half of the prosthesis form a "U" -shaped opening towards the top, in the extension the patella on the front leg and the platform abut the bottom of this "U", while in flexion the bottom under the patella and the rear leg to Platform turns. Both forces from the patella from the front and forces from behind occur on the femoral stump when flexed from the platform, which are intercepted by opposing, approximately mutually perpendicular resection surfaces. In most upper prosthesis parts, the associated outer contact surfaces are at a small angle to each other, so that when pushed by the wedge effect a tight fit is achieved to the denture stump. For many Asian residents, the flexion angle achievable with such a prosthesis is insufficient because they are inherently accustomed to living at a greater flexion angle and bring a knee prosthesis into flexion angles for which the latter are not suitable.

In FR-A-2768329, the femoral component has a central part with guide surfaces for the patella and a condyle part separately slidable thereon which has outer abutment surfaces at an acute angle β ≤ 90 ° and which along a straight line in the swivel range of the angle β on resection surfaces at the stump of the femur is pushed. The object of the invention is to show construction forms that allow large angles of flexion in an open joint. This object is achieved in that the center line of the angle β is pivoted on the condyle part with respect to the center line of the angle α at the central part by an angle 15 ° ≤ γ ≤ 60 ° to allow greater flexion.

The advantage of the invention is that even with great flexion, the forces that are transmitted through the prosthesis shell on the prosthesis stump are compressive forces. There are no shear loads between contact surfaces and resection surfaces, which are opposite to the Aufschieberichtung. Due to the fact that the upper part of the prosthesis is in a central part and is divided into a condyle part, the parting line extends so that the guide surfaces for the patella are arranged in the middle part and treads to the platform on the condyle part are arranged, these surfaces can be made independently and pushed independently in mutually pivoted Aufschieichtung on the femoral stump become. Despite different Aufschieregungen can contact surfaces of the middle part and the condyle share together on a Resektionsfläche. The Aufschieregungen are, for example, by an angle γ between 15 ° and 60 ° pivoted to allow a large flexion angle δ. In this case, flexion angles δ of more than 120 °, for example 160 °, are possible. The condyles may be connected to a yoke or carried out individually. In the deferred state, the condyles are aligned through the resection surfaces, ie via the femoral stump to the middle part. In addition, midsection and condyle parts may be movably guided in sagittal planes to provide similar patellar and platform force application points to the femur stump as in a natural knee joint. But it is also possible to connect the middle part and condyle by a coupling member in the pushed state.

For attachment with bone cement individual contact surfaces may have pockets to bring a minimum amount of bone cement. Individual contact surfaces, in particular the outer contact surfaces, can have a toothed anchoring structure for a primary anchoring. Likewise, individual pins which extend in Aufschieberichtung and are provided for in the direction of insertion holes, improve the primary anchorage. The non-bone cement-wetted contact surfaces may be coated with a coating that promotes bone growth.

Bearing surfaces which are wetted by bone cement may be coated with a bonding agent. Such a coating may for example be composed of a Titanalalkoholat and an alkoxysilane.

During flexion, the engaged radius of curvature of the condyles may continuously or sharply decrease to interfere with increasing flexion to allow lateral deflection of the condyles.

Fig. 1:

schematisch einen Femurstumpf mit vorbearbeiteten Resektionsflächen, auf den ein gemäss

Fig. 2:

schematisch gezeigtes Mittelteil entlang einer Mittellinie aufschiebbar ist und ein gemäss

Fig. 3:

schematisch gezeigtes Kondylenteil entlang einer um einen Winkel γ verschwenkten Mittellinie aufschiebbar ist;

Fig. 4:

schematisch eine Ansicht für ein weiteres Beispiel von einem Mittelteil;

Fig. 5:

schematisch ein zu Figur 4 passendes Kondylenteil mit einem Joch;

Fig. 6:

schematisch eine Seitenansicht von Figur 4;

Fig. 7:

schematisch eine Seitenansicht von Figur 5;

Fig. 8:

schematisch eine Ansicht von unten der Figuren 4 und 5 vor dem Aufschieben

Fig. 9:

schematisch Mittelteil und Kondylenteil von Figur 8 nach dem Aufschieben

Fig. 10:

schematisch eine Ansicht von einem Mittelteil mit zwei voneinander unabhängigen Kondylen vor dem Aufschieben;

Fig. 11:

schematisch unter einem etwas anderen Blickwinkel die Teile von Figur 10 nach dem Aufschieben; und

Fig. 12:

schematisch einen vergrösserten Ausschnitt einer äusseren Anlagefläche mit einer Zahnung für die Primärverankerung.

In the following the invention will be described by means of embodiments. Show it:

Fig. 1:

schematically a Femurstumpf with pre-machined resection surfaces on the one according

Fig. 2:

schematically shown middle part along a center line can be pushed and a according to

3:

schematically shown condyle part can be pushed along a center line pivoted by an angle γ;

4:

schematically a view of another example of a central part;

Fig. 5:

schematically a matching to Figure 4 condyle part with a yoke;

Fig. 6:

schematically a side view of Figure 4;

Fig. 7:

schematically a side view of Figure 5;

Fig. 8:

schematically a bottom view of Figures 4 and 5 before pushing

Fig. 9:

schematically middle part and condyle part of Figure 8 after pushing

Fig. 10:

schematically a view of a central part with two independent condyles before pushing on;

Fig. 11:

schematically from a slightly different angle, the parts of Figure 10 after sliding; and

Fig. 12:

schematically an enlarged section of an outer contact surface with a toothing for the primary anchorage.

The figures show femoral parts of knee prostheses which have a central part 2 and a condyle part 3 with abutment surfaces 4a, 5a, 6a, 6b, 7b, 8a, 9a, 10a, 11a, 11b, 12a, 12b, 13b to form a resected femoral stump 1 , In this case, the middle part 2 has guide surfaces 20 for a patella 19 and outer contact surfaces 4a, 5a which are at an acute angle α ≤ 90 ° to each other, while the condyle part 3 running surfaces 27, 28 for the articulation movement and outer abutment surfaces 6b, 7b at an acute angle β ≤ 90 ° to each other. Middle part 2 and condyle part 3 are separately on the femur stump in mutually pivoted Aufsteckrichtungen attachable to allow greater flexion, wherein the center line of the angle β relative to the center line of the angle α by an angle 15 ° ≤ γ ≤ 60 ° is pivoted.

In the following the same signs are used for the same functions.

In the example of FIGS. 1, 2 and 3, resection surfaces 4, 6, 11, 12, 12, 13, 7 and in the region between the condyles resection surfaces 4, 8, 9, 10, 5 are attached to a femoral stump 1 in the region of the condyles. The resection surfaces 4 and 5 as well as the outer abutment surfaces 4a, 5a of the middle part 2 adjoining them are almost parallel to one another at an acute angle. The middle part is supported by the contact surfaces 8a, 9a, 10a between the condyles and with further contact surfaces 6a, 11a, 12a on resection surfaces in the region of the former natural condyles, these resection surfaces also occupied by contact surfaces 6b, 11b, 12b of the condyle part 3 to center in the trench between the condyles and to provide support for the patellar guide surfaces 20 even with complete flexion.

The middle part is attachable from below along the center line 15 of the angle α, while the Aufsteckrichtung and the center line 16 of the angle β is pivoted by an angle γ of 45 ° to even at a larger flexion angle δ, for example δ> 120 °, an outer bearing surface 7b, in which the contact force presses the surface 7b into the stump or at most perpendicular to the surface 7b. As can be seen from FIG. 3, the running surface 27 of the condyle part 3 and the running surface 18 of a meniscus part 18 have the same radius of curvature R ₁ .

Another example is shown in Figures 4, 5, 6, 7, 8, 9. Again, because of the increased flexion angle, the guide surfaces 20 for the patella 19 and the treads 27, 28 are extended in the direction of flexion. The middle part 2 has abutment surfaces 4a, 6a, 8a, 11a, 5a and lateral centering surfaces 31. The condyle part 2 has a yoke 14 which connects the actual condyles. A parting line 25 between the middle part 2 and the condyle part 3 is laid (FIGS. 8, 9) so that the guide surfaces 20 for the patella 19 and the running surfaces 27, 28 of the condyles are not interrupted. A recess 24 is provided for cruciate ligaments. A portion of the abutment surfaces 4a, 6a, 8a, 11a has pockets 17, which are filled with bone cement when pushed on to allow a minimum layer thickness of bone cement in certain areas. The pockets 17 and abutment surfaces may also be pre-cemented with a primer and a thin layer of bone cement.

According to the acute angle .alpha. In FIG. 6, the center part 2 must be slid open approximately in the direction of the center line 15, whereas in the case of the condyle part with a less acute angle .beta. A greater deviation of the pushing direction from the center line of the angle .beta. Is possible. Here, the Aufschieberichtung, which must be within the angle β, determined by the direction of the pins 23. In FIGS. 5 and 7, a generatrix for the contour of the condyle running surfaces 27, 28 is indicated. The radius of curvature R _{1 of} the running surfaces 27, 28 merges with increasing flexion into a smaller radius of curvature R ₂ .

Middle part 2 and condyle part 3 have holes 22, so that they can be connected to a femoral stub with a coupling piece in the form of a pin 32 after plugging. Due to this composite, the femoral stump is trapped at the same time because it is enclosed by contact surfaces at a wrap angle of more than 180 °.

In FIG. 12, the detail of the abutment surface 4a shows that in the case of outer abutment surfaces which face each other at a very acute angle, such as in FIG. 6, the surfaces 4a and 5a, it may be expedient to provide this surface with a toothing which has a tooth surface good primary anchorage allows and secures the middle part 2 until the condyle part 3 is attached.

The example of Figures 10 and 11, an arrangement is shown in which two separate condyle parts 3 with treads 27, 28 are attachable and can be connected via holes 22 by a coupling piece, such as a pin or a screw with the middle part 2. If the ligaments on the knee allowed, these two condyle parts 3 can also be introduced from the side, since they are not firmly connected to a yoke, then - depending on how long the pins 23 are designed - in the direction of the pins their To find anchoring. As soon as a condyle part 3 is connected to the middle part 2, the femur stump is enclosed here at an angle of wrap of more than 180 ° and, without risk, a flexion angle of more than 120 ° is possible.

Claims (14)

1. A knee prosthesis having a femur part which has guide surfaces (20) for a patella (19) and at least one condyle (18), which has outer contact surfaces (4a, 5a) at an acute angle α ≤ 90° and whose contact surfaces can be pushed onto resection areas (4, 5, 6, 8, 9, 10, 11, 12) at the stump of a femur bone (1) along a straight line in the pivot range of the angle α, wherein the femur part has a centre part (2) with guide surfaces (20) for the patella (19) and a condyle part (3) which can be pushed on separately therefrom, which has outer contact surfaces (6b, 7b) at an acute angle β ≤ 90° and which can be pushed onto resection areas (6, 7, 11, 12, 13) at the stump of the femur bone along a straight line in the pivot range of the angle β, characterised in that the centre line (16) of the angle β at the condyle part (3) is pivoted through an angle of 15° ≤ γ ≤ 60° with respect to the centre line (15) of the angle α at the centre part (2) in order to allow a greater flexion.
2. A knee prosthesis in accordance with claim 1, characterised in that the condyle part (3) has a flexion angle δ of more than 120°.
3. A knee prosthesis in accordance with claim 1 or claim 2, characterised in that the condyle part (3) has two condyles (3) each outwardly disposed with respect to the centre part (2) which are connected via a yoke (14).
4. A knee prosthesis in accordance with any of claims 1 to 3, characterised in that the centre part (2) and the condyle part (3) are connectable to one another by a coupling member (21) in the pushed-on state.
5. A knee prosthesis in accordance with claim 4, characterised in that the coupling member (21) consists of a pin inserted transversely through separating surfaces or of a transversely throughgoing screw connection.
6. A knee prosthesis in accordance with any one of claims 1 to 5, characterised in that the angle γ is between 40° and 50°.
7. A knee prosthesis in accordance with any of claims 1 to 6, characterised in that individual contact surfaces (4a, 5a, 6a, 6b, 7b, 8a, 9a, 10a, 11a, 11b, 12a, 12b, 13b) have pockets (17) in order to introduce a minimum quantity of bone cement for a fastening with bone cement.
8. A knee prosthesis in accordance with any one of claims 1 to 6, characterised in that individual contact surfaces (4a, 5a, 6a, 6b, 7b, 8a, 9a, 10a, 11a, 11b, 12a, 12b, 13b) have a serrated anchoring structure (30) for a primary anchoring.
9. A knee prosthesis in accordance with any of claims 1 to 6, characterised in that individual contact surfaces (4a, 5a, 6a, 6b, 7b, 8a, 9a, 10a, 11a, 11b, 12a, 12b, 13b) are covered with a coating which promotes bone growth or enhances the adhesion of bone cement.
10. A knee prosthesis in accordance with claim 9, characterised in that the film contains substances such as hydroxyl appatite or is made up of a titanal alcoholate and an alkoxy silane.
11. A knee prosthesis in accordance with any of claims 1 to 10, characterised in that the radius of curvature R₁ of the condyles (3) is reduced at least once in the contact region from the transition of the extension to the full flexion.
12. A knee prosthesis in accordance with any of claims 1 to 11, characterised in that the angle α or β is less than 10°.
13. A knee prosthesis in accordance with any of claims 1 to 11, characterised in that the angle α or β is less than 5°.
14. A knee prosthesis in accordance with any of claims 1 to 13, characterised in that spigots (23) are attached to contact surfaces (12b) in the direction of pushing on which facilitate centering and primary anchoring.

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